Semiconductor circuit with metal structure having different pitches

ABSTRACT

The semiconductor structure includes a semiconductor substrate having active regions; field-effect devices disposed on the semiconductor substrate, the field-effect devices including gate stacks with elongated shape oriented in a first direction; a first metal layer disposed over the gate stacks, the first metal layer including first metal lines oriented in a second direction being orthogonal to the first direction; a second metal layer disposed over the first metal layer, the second metal layer including second metal lines oriented in the first direction; and a third metal layer disposed over the second metal layer, the third metal layer including third metal lines oriented in the second direction. The first, second, and third metal lines have a first thickness T 1 , a second thickness T 2 , and t a third thickness T 3 , respectively. The second thickness is greater than the first thickness and the third thickness.

PRIORITY DATA

The present application is a divisional application of U.S. patentapplication Ser. No. 15/964,216, files Apr. 27, 2018, which claimspriority to U.S. Provisional Patent Application No. 62/611,037 filedDec. 28, 2017, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND

In semiconductor process development, it is usually required waferacceptance test (WAT) at a lower level metal layer (such as the 1^(st)or 2^(nd) level metal layer) to have quick feedback on both deviceperformance and process margin. However, this will face a testrobustness problem when the technology and metal pitcher continuouslyscale down to smaller feature sizes in advanced technology nodes.Therefore it requires the metal thickness (depth) thinner to maintainmetal trench aspect ratio (depth/width) to have enough process marginsfor various fabrication processes (such as etching and metal deposition)during the formation of the corresponding metal layer. For example,during the formation of metal lines in this metal layer by a damasceneprocess, it is challenge to etch an interlayer dielectric material toform trenches and vias with high aspect ratios when the metal layer isthick. Furthermore, it is challenge to deposit a metal in the trenchesand/vias with high aspect ratio. On other side, a thinner metal layereasily causes WAT test failure due to various factors, such as highcontact resistance or open, or probe punching through the test pads.Thinner metal layer is also conflicted with lower level metal testrequirement.

Packing density is also a challenge when the semiconductor is scaleddown to small feature sizes. For example, a logic circuit includesvarious logic gates, such as inverters, NAND gates, AND gates, NOR gatesand flip-flop. In deep sub-micron integrated circuit technology, thelogic circuit progressed to smaller feature sizes for higher packingdensity. However, the existing structure of a logic circuit still hasvarious aspects to be improved for its performance and further enhancedpacking density.

It is therefore desired to have an integrated circuit design andstructure, and the method making the same to address the above issueswith increased packing density.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a sectional view of a semiconductor structure constructedaccording to various aspects of the present disclosure in oneembodiment.

FIG. 2 is a top view of an interconnection gate and the metal lines inthe semiconductor structure of FIG. 1, in accordance with someembodiments.

FIGS. 3, 4 and 5 are sectional views of a gate in the semiconductorstructure of FIG. 1, in accordance with some embodiments.

FIG. 6 is a sectional view of a contact in the semiconductor structureof FIG. 1, in accordance with some embodiments.

FIGS. 7 and 8 are sectional views of a via feature in the semiconductorstructure of FIG. 1, in accordance with some embodiments.

FIG. 9 is a top view of gate stacks and second metal lines constructedin accordance with some embodiments.

FIG. 10 is a sectional view of a semiconductor structure having at leastsix metal layers, in accordance with some embodiments.

FIGS. 11A, 11B and 11C are top views of a semiconductor structure havingan inverter, a logic NAND gate cell and a logic NOR gate cell, atvarious stages, in accordance with some embodiments.

FIG. 12 is a schematic view of an inverter, a logic NAND gate and alogic NOR gate cell, in accordance with some embodiments.

FIG. 13 is a top view of a semiconductor structure having an inverter, alogic NAND gate cell and a logic NOR gate cell, in accordance with someembodiments.

FIG. 14 is a top view of a semiconductor structure having an inverter inaccordance with some embodiments.

FIG. 15 is a top view of a semiconductor structure having an array ofstandard circuit cells in accordance with some embodiments.

FIG. 16 is a schematic view of a flip-flop cell in accordance with someembodiments.

FIG. 17 is a sectional view of the semiconductor structure of FIG. 1, inportion, constructed in accordance with some embodiments.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 is a sectional view of a semiconductor structure 100 constructedaccording to various aspects of the present disclosure in oneembodiment. In some embodiments, the semiconductor structure 100 isformed on fin active regions and includes fin field-effect transistors(FinFETs). In some embodiments, the semiconductor structure 100 isformed on flat fin active regions and includes effect transistors(FETs). In various embodiments, the semiconductor structure 100 includesone or more standard cell to be incorporated and repeatedly used tointegrated circuit designs. Those standard cells may include variousbasic circuit devices, such as inverter, NAND, NOR, AND, OR, andflip-flop, which are popular in digital circuit design for applications,such as central processing unit (CPU), graphic processing unit (GPU),and system on chip (SOC) chip designs. In the present embodiment, thesemiconductor structure 100 includes a standard cell defined in thedashed lines 101.

The semiconductor structure 100 includes a semiconductor substrate 102.The semiconductor substrate 102 includes silicon. Alternatively, thesubstrate 102 may include an elementary semiconductor, such as siliconor germanium in a crystalline structure; a compound semiconductor, suchas silicon germanium, silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;or combinations thereof. Possible substrates 102 also include asilicon-on-insulator (SOI) substrate. SOI substrates are fabricatedusing separation by implantation of oxygen (SIMOX), wafer bonding,and/or other suitable methods.

The substrate 102 also includes various isolation features, such asisolation features 104 formed on the substrate 102 and defining variousactive regions on the substrate 102, such as an active region 106. Theisolation feature 104 utilizes isolation technology, such as shallowtrench isolation (STI), to define and electrically isolate the variousactive regions. The isolation feature 104 includes silicon oxide,silicon nitride, silicon oxynitride, other suitable dielectricmaterials, or combinations thereof. The isolation feature 104 is formedby any suitable process. As one example, forming STI features includes alithography process to expose a portion of the substrate, etching atrench in the exposed portion of the substrate (for example, by using adry etching and/or wet etching), filling the trench (for example, byusing a chemical vapor deposition process) with one or more dielectricmaterials, and planarizing the substrate and removing excessive portionsof the dielectric material(s) by a polishing process, such as a chemicalmechanical polishing (CMP) process. In some examples, the filled trenchmay have a multilayer structure, such as a thermal oxide liner layer andfilling layer(s) of silicon nitride or silicon oxide.

The active region 106 is a region with semiconductor surface whereinvarious doped features are formed and configured to one or more device,such as a diode, a transistor, and/or other suitable devices. The activeregion may include a semiconductor material similar to that (such assilicon) of the bulk semiconductor material of the substrate 102 ordifferent semiconductor material, such as silicon germanium (SiGe),silicon carbide (SiC), or multiple semiconductor material layers (suchas alternative silicon and silicon germanium layers) formed on thesubstrate 102 by epitaxial growth, for performance enhancement, such asstrain effect to increase carrier mobility.

In some embodiments, the active region 106 is three-dimensional, such asa fin active region extended above the isolation feature 104. The finactive region is extruded from the substrate 102 and has athree-dimensional profile for more effective coupling between thechannel and the gate electrode of a FET. The fin active region 106 maybe formed by selective etching to recess the isolation features 104, orselective epitaxial growth to grow active regions with a semiconductorsame or different from that of the substrate 102, or a combinationthereof.

The semiconductor substrate 102 further includes various doped features,such as n-type doped wells, p-type doped wells, source and drainfeatures, other doped features, or a combination thereof configured toform various devices or components of the devices, such as source anddrain features of a field-effect transistor. The semiconductor structure100 includes various IC devices 108 formed on the semiconductorsubstrate 102. The IC devices includes fin field-effect transistors(FinFETs), diodes, bipolar transistors, imaging sensors, resistors,capacitors, inductors, memory cells, or a combination thereof. In FIG.1, exemplary FETs are provided only for illustration.

The semiconductor structure 100 further includes various gates (or gatestacks) 110 having elongated shape oriented in a first direction (Xdirection). In the present embodiment, X and Y directions are orthogonaland define a top surface 112 of the semiconductor substrate 102. A gateis a feature of a FET and functions with other features, such assource/drain (S/D) features and a channel, wherein the channel is in theactive region and is directly underlying the gate; and the S/D featuresare in the active region and are disposed on two sides of the gate.

The semiconductor structure 100 also includes one or moreinterconnection gate 114 formed on the substrate 102. Theinterconnection gate 114 also has an elongated shape oriented in the Xdirection. The interconnection gate 114 is similar to the gate 110 interms structure, composition and formation. For example, the gates 110and the interconnection gate 114 are collectively and simultaneouslyformed by a same procedure, such as a gate-last process. However, theinterconnection gate 114 is disposed and configured differently andtherefore functions differently. In the present embodiment, theinterconnection gate 114 is at least partially landing on the isolationfeature 104. For example, the interconnection gate 114 is partiallylanding on the active region 106 and partially landing on the isolationfeature 104. The interconnection gate 114 therefore provides isolationfunction between adjacent IC devices and additionally provides patterndensity adjustment for improved fabrication, such as etching, depositionand chemical mechanical polishing (CMP). In the present embodiment, theinterconnection gates 114 or a subset thereof are formed on the boundarylines between the adjacent standard cells. Furthermore, theinterconnection gate 114 is connected to metal lines through gatecontacts and therefore functions as a local interconnection as well.This is illustrated in FIG. 2 and described in details. FIG. 2 is a topview of the semiconductor structure 100, in portion, in accordance withsome embodiments.

In FIG. 2, the contact features 116 are disposed on two ends of theinterconnection gate 114 and directly landing on the interconnectiongate 114. Those contacts 116 are further connected to metal lines 118.Thus, the interconnection gate 114 functions as a local interconnectionfeature to contribute to the interconnection structure, which will befurther described later.

Referring back to FIG. 1, the gates 110 and the interconnection gate 114have same compositions and formed by a same procedure. The structure ofthe gates 110 and the interconnection gates 114 is further describedwith reference to FIGS. 3-5 of a gate 120 in sectional view, accordingto various embodiments. The gate 120 represents both the gates 110 andthe interconnection gate 114 since both are formed in a same procedureand have a same structure. The gate 120 includes a gate dielectric layer122 (such as silicon oxide) and a gate electrode 124 (such as dopedpolysilicon) disposed on the gate dielectric layer, as illustrated inFIG. 3.

In some embodiments, the gate 120 alternatively or additionally includesother proper materials for circuit performance and manufacturingintegration. For example, the gate dielectric layer 122 includes aninterfacial layer 122A (such as silicon oxide) and a high k dielectricmaterial layer 122B, as illustrated in FIG. 4. The high k dielectricmaterial may include metal oxide, metal nitride or metal oxynitride. Invarious examples, the high k dielectric material layer includes metaloxide: ZrO2, Al2O3, and HfO2, formed by a suitable method, such as metalorganic chemical vapor deposition (MOCVD), physical vapor deposition(PVD), atomic layer deposition (ALD), or molecular beam epitaxy (MBE).In some examples, the interfacial layer includes silicon oxide formed byALD, thermal oxidation or ultraviolet-Ozone Oxidation. The gateelectrode 124 includes metal, such as aluminum, copper, tungsten, metalsilicide, doped polysilicon, other proper conductive material or acombination thereof. The gate electrode may include multiple conductivefilms designed such as a capping layer, a work function metal layer, ablocking layer and a filling metal layer (such as aluminum or tungsten).The multiple conductive films are designed for work function matching ton-type FET (nFET) and p-type FET (pFET), respectively. In someembodiments, the gate electrode for nFET includes a work function metalwith a composition designed with a work function equal 4.2 eV or lessand the gate electrode for pFET includes a work function metal with acomposition designed with a work function equal 5.2 eV or greater. Forexamples, the work function metal layer for nFET includes tantalum,titanium aluminum, titanium aluminum nitride or a combination thereof.In other examples, the work function metal layer for pFET includestitanium nitride, tantalum nitride or a combination thereof.

In some embodiments illustrated in FIG. 5, the gate 120 is formed by adifferent method with a different structure. The gate may be formed byvarious deposition techniques and a proper procedure, such as gate-lastprocess, wherein a dummy gate is first formed, and then is replaced by ametal gate after the formation the source and drain features.Alternatively, the gate is formed by a high-k-last a process, whereinthe both gate dielectric material layer and the gate electrode arereplaced by high k dielectric material and metal, respectively, afterthe formation of the source and drain features. In a high-k-lastprocess, a dummy gate is first formed by deposition and patterning; thensource/drain features are formed on gate sides and an inter-layerdielectric layer is formed on the substrate; the dummy gate is removedby etching to result in a gate trench; and then the gate material layersare deposited in the gate trench. In the present example, the gateelectrode 124 includes a work function metal layer 124A and a fillingmetal, such as aluminum or copper. Thus formed gate 120 has various gatematerial layers U-shaped.

Referring back to FIG. 1, the semiconductor structure 100 also includesmultilayer interconnection (MLI) structure 130 designed and configuredto couple various field-effect transistors and other devices to form anintegrated circuit having various logic gates, such as inverters, NANDgates, NOR gates, AND gates, OR gates, flip-flops, or a combinationthereof. It is noted that various logic gates each may include multiplefield-effect transistors and each FET includes a source, a drain and agate 110. The gate 110 should not be confused with a logic gate. Forclarification, sometime, the gate 110 is also referred to as transistorgate.

The MLI structure 130 includes a first metal layer 132, a second metallayer 134 over the first metal layer 132 and a third metal layer 136over the second metal layer 134. Each metal layer includes a pluralityof metal lines, such as first metal lines (“M1”) in the first metallayer 132, second metal lines (“M2”) in the second metal layer 134, andthird metal lines (“M3”) in the third metal layer 136. The MLI structure130 may include more metal layers, such as a fourth metal layer, fifthmetal layer, and so on. In the present embodiments, the metal lines ineach layer are oriented in a same direction. Specifically, the firstmetal lines are oriented in the Y direction, the second metal lines areoriented in the X direction and the third metal lines are oriented inthe X direction. The metal lines in different metal layers are connectedthrough vertical conductive features (also referred to as vias or viafeatures). The metal lines are further coupled to the semiconductorsubstrate 102 (such as source and drain features) through verticalconductive features. In the present embodiment, the S/D features areconnected to the first metal lines through contact features (“contact”)116 and 0^(th) via features (“Via-0”) 142. Furthermore, the first metallines 132 are connected to the second metal lines 134 through first viafeatures (“Via-1”) 144; and the second metal lines 134 are connected tothe third metal lines 136 through second vias features (“Via-2”) 146.

Among those contacts and via features, both the contacts 116 and thevia-0 features 142 are conductive features to provide verticalinterconnection paths between the substrate 102 and the first metallines 132 but they are different in terms of composition and formation.The contacts 116 and the via-0 features 142 are formed separately. Forexamples, the contacts 114 are formed by a procedure that includespatterning an interlayer dielectric (ILD) layer to form contact holes;depositing to fill in the contact holes to form contacts; and mayfurther include a chemical mechanical polishing (CMP) to remove thedeposited metal materials from the ILD layer and planarize the topsurface. The via-0 features 142 are formed by an independent procedurethat includes a similar procedure to form the contacts 116 oralternatively a dual damascene process to collectively form the Via-0features 142 and the first metal lines 132. In some embodiments, thecontacts 116 include a barrier layer 150 and a first metal materiallayer 152, as illustrated in FIG. 6 in a sectional view; and the Via-0features 142 include a barrier layer 150 and a second metal materiallayer 154, as illustrated in FIG. 7. In various examples, the barrierlayer 150 includes titanium, titanium nitride, tantalum, tantalumnitride, other suitable material, or a combination thereof; the firstmetal material layer 152 includes cobalt; the second metal materiallayer 154 includes ruthenium, cobalt, copper, or a combination thereof.In the present embodiment, the barrier layer 150 includes a dual filmscheme with a first barrier film 150A and a second barrier film 150B.

In one embodiment, the first metal material layer 152 includes cobalt;the second metal material layer includes tungsten; and the barrier layer150 includes the first barrier film 150A of tantalum nitride and thesecond barrier film 150B of tantalum film. In another embodiment, thevia-0 features 142 are collectively formed with the first metal lines132 in a dual-damascene process, in which the via-0 features 142 (andthe first metal lines 132 as well) include the barrier layer 150 and thesecond metal material layer 154 of copper (or copper aluminum alloy).

In yet another embodiment, the via-0 features 142 include only tungsten,as illustrated in FIG. 8. In some other embodiments where both the via-0features 142 and the first metal lines 132 are formed by adual-damascene process, both the via-0 features 142 and the first metallines 132 includes a material layer stack of a titanium nitride film,titanium film, and cobalt; or a material stack of a titanium nitridefilm, a titanium film, and a ruthenium film; or a material film stack ofa tantalum nitride film and a copper film.

The semiconductor structure 100 also includes some test structures forwafer acceptance test (WAT). In the existing method, WAT test structuresare formed on the first and/or second metal layers. However, as notedabove, this has issues on test robustness when the technology and metalpitcher continuously scale down to smaller sizes in advanced technologynodes. When the metal layer is thick, trenches have aspect ratio(depth/width) too larger to be properly filled and it is also harder toetch a trench with a large aspect ratio. When the metal layer is thin,it can easily cause WAT test failure, such as high contact resistance oropen, or probe punching through the test pads.

In the disclosed MLI structure 130, the metal layers are designed withthe various parameters to overcome these concerns. In the MLI structure130, various metal layers are designed with thicknesses, widths, andpitches to be compatible with test structure and have standard cellswith improved packing density, which is described below in details. Themetal lines in different layers have different dimensional parameters.Particularly, the first metal lines have a first thickness T₁, thesecond metal lines have a second thickness T₂, and the third metal lineshave a third thickness T₃. The second thickness T₂ is greater than thefirst thickness T₁ and the third thickness T₃. In the presentembodiment, a first thickness ratio T₂/T₁ and a second thickness ratioT₂/T₃ both are equal to or greater than 1.2; and a third thickness ratioT₃/T₁ is designed to be 1. In the disclosed structure, those parametersand other subsequently introduced parameters are provided with designvalues or ranges. The manufactured circuits may experience smallvariation, such as less than 5% variation. In some embodiments, thefirst thickness ratio T₂/T₁ and second thickness ratio T₂/T₃ both rangebetween 1.2 and 2. In yet some other embodiments, the first thicknessratio T₂/T₁ and second thickness ratio T₂/T₃ both range between 1.3 and1.8. The ratios are constrained in those ranges such that to effectivelyincrease the routing efficiency and the chip packing density on one sideand decrease the intra-cell coupling capacitance and the power linesresistance on another side.

The pitches and widths of various features are further described below.The gates 110 have a minimum pitch P_(g); the first metal lines 132 havea minimum pitch P₁; the second metal lines 134 have a minimum pitch P₂;and the third metal lines 136 have a minimum pitch P₃. The gates 110have a width W_(g); the first metal lines 132 have a width W₁; thesecond metal lines 134 have a width W₂; and the third metal lines 136have a width W₃. The gates 114 and the second metal lines 134 arefurther illustrated in FIG. 9 in a top view. A pitch of features isdefined as the dimension between two adjacent features (measured fromsame locations, such as center to center, or left edge to left edge).For examples, the gate pitch is the dimension from one gate to anadjacent gate, and the second metal line pitch is the dimension from oneto an adjacent one of the second metal lines. Since pitch may not be aconstant, the minimum pitch is defined and constrained above in thedisclosed structure. Both the gates 110 and the second metal lines 134are oriented in the X direction. The first metal lines and the thirdmetal lines are oriented in the Y direction. In the present embodiment,the gates 114 and the second metal lines 134 have a same minimum pitchbut different widths. Particularly, the first pitch ratio P_(g)/P₂ is 1but W₂ usually does not equal to W_(g); and the first metal lines 132and the third metal lines 136 have a same minimum pitch or the secondpitch ratio P₃/P₁ is 1 in other words. In some examples, the minimumpitch of the gates 110 is determined when the gates 110 and theinterconnection gates 114 are collectively considered. Furthermore, theminimum pitch of the second metal lines 134 is greater than the minimumpitch P₁ of the first metal lines 132 and the minimum pitch P₃ of thethird metal lines 136. A third pitch ratio P₂/P₃ (P₂/P₁ as well) isgreater than 1. By utilizing the disclosed structure, the second metallines 134 have a large thickness and large minimum pitch. Thus, theaspect ratio of the second metal lines 134 is reduced by the increasedminimum pitch and the thickness of the second metal lines 134. The teststructures formed in the second metal layer have WAT test robustness dueto large thickness and enough processing margin due to the increasedaspect ratio. In the present embodiment, the power lines (such as V_(dd)and V_(ss)) are routed in the second metal lines 134, taking theadvantages of the greater dimensions and less resistance of the secondmetal lines 134. The power line routing includes horizontal routing ofthe power lines being substantially distributed in the second metallines 134.

Other advantages may present in various embodiments of the semiconductorstructure 100. For examples, with the reduced thicknesses and pitches ofthe first metal lines 132 and the third metal lines 136; the routingefficiency is increased; the intra-cell coupling capacitance and thepower lines resistance are reduced; chip packing density is increased;large pitches are minimized due to the minimum pitch of the second metallines 134 are substantially aligned with that of the gates 110; and thecircuit speed is improved.

FIG. 10 is a sectional view of a semiconductor structure 160 constructedaccording to various aspects of the present disclosure in oneembodiment. The semiconductor structure 160 is similar to thesemiconductor structure 100 in FIG. 1 but includes at least six metallayers.

In some embodiments, the semiconductor structure 160 is formed on finactive regions and includes FinFETs. In some embodiments, thesemiconductor structure 160 is formed on flat active regions andincludes FETs. In various embodiments, the semiconductor structure 160includes one or more standard cell to be incorporated and repeatedlyused in integrated circuit designs. In the present embodiment, thesemiconductor structure 160 includes two standard cells (“C1” and “C2”)defined by the dashed lines 161. Those standard cells may includevarious basic circuit devices, such as inverter, NAND, NOR, AND, OR, andflip-flop, which are popular in digital circuit design for applications,such as central processing unit (CPU), graphic processing unit (GPU),and system on chip (SOC) chip designs.

The metal lines in different layers have different dimensionalparameters. Similar to the semiconductor structure 100, thesemiconductor structure 160 includes the first metal lines 132, thesecond metal lines 134, the third metal lines 136 and the variouscontact and via features. Particularly, the first metal lines have afirst thickness T₁, the second metal lines have a second thickness T₂,and the third metal lines have a third thickness T₃. The secondthickness T₂ is greater than the first thickness T₁ and the thirdthickness T₃. In the present embodiment, a first thickness ratio T₂/T₁and a second thickness ratio T₂/T₃ both are equal to or greater than1.2; and a third thickness ratio T₃/T₁ is designed to be 1. In thedisclosed structure, those parameters and other subsequently introducedparameters are provided with design values or ranges. The manufacturedcircuits may experience small variation, such as less than 5% variation.In some embodiments, the first thickness ratio T₂/T₁ and secondthickness ratio T₂/T₃ both ranges between 1.2 and 2. In yet some otherembodiments, the first thickness ratio T₂/T₁ and second thickness ratioT₂/T₃ both ranges between 1.3 and 1.8.

Furthermore, the gates 110 and the second metal lines 134 are aligned tohave a same minimum pitch. Again the minimum pitch of the gates isdetermined when the gates 110 and interconnection gates 114 arecollectively considered, according to some embodiments. In the presentembodiment illustrated in FIG. 10, the interconnection gates 114 or asubset thereof are formed on the boundary lines 161 between the adjacentstandard cells.

Furthermore, the semiconductor structure 160 includes a fourth metallines 162, the fifth metal lines 164, the sixth metal lines 166 and thevarious via features, such as third via features 172, fourth viafeatures 174, and fifth via features 176. Particularly, the fourth metallines 162 have a fourth thickness T₄, the fifth metal lines 164 have afifth thickness T₅, and the sixth metal lines have a sixth thickness T₆.The fifth thickness T₅ is designed to equal to the sixth thickness T₆.Again, the manufactured thickness may have certain variation, such asless than 5%. The fifth thickness T₅ is designed to be greater than thesecond thickness T₂. In the present embodiment, a thickness ratio T₅/T₂is equal to or greater than 1.2.

The third via features (“Via-3”) 172 have a width Wv₃, the fourth viafeatures (“Via-4”) 174 have a width Wv₄, and the fifth via features(“Via-5”) 176 have a width Wv₅. In the present embodiment, the width Wv₅is greater than the width Wv₄, such as with a ratio Wv₅/Wv₄ being 1.5 orgreater to have increased packing density and decreased line resistance.In some embodiments, the via features in a same layer may have differentwidth or variation. In this case, the above widths are minimum widthsand the width ratio is the ratio of the corresponding minimum widths.

FIGS. 11A, 11B and 11C are top views of an integrated circuit 180constructed according to various aspects of the present disclosure inone embodiment. As so many features are overlapped with each other, afirst few layers (fin active regions and gates) are illustrated in FIG.11A. The contact features 116, the via-0 features 142 and the firstmetal lines 132 are added to FIG. 11B. The via-1 features 144, thesecond metal lines 134, the via-2 features 146, and the third metallines 136 are added to FIG. 11C. FIGS. 11A and 11B help comprehendvarious features and the layout of the integrated circuit 180. Theintegrated circuit 180 is one embodiment of the semiconductor structure100 or the semiconductor structure 160. Various metal lines and gatesare oriented, configured and designed with dimension as described in thesemiconductor structure 100 or 160. For example, the thickness of thesecond metal lines 134 is greater than the thickness of the first metallines 132 and the thickness of the third metal lines 136.

The integrated circuit 180 includes various standard cells configured ina layout illustrated in FIG. 11A. The integrated circuit 180 includesmultiple standard cells integrated in a layout illustrated in FIG. 11A.The boundary lines of those standard cells are presented by the dashedlines 182. In the present embodiment, the integrated circuit 180includes a first standard cell 184 having an inverter; a second standardcell 186 having an NAND logic gate; and a third standard cell 188 havinga NOR logic gate. Each standard cell includes at least one nFET (“nFET”)and at least one pFET (“pFET”). Note that a logic gate is a circuitincluding multiple devices (such as multiple FETs) and is different froma gate in a FET.

Referring back to FIG. 11A, various standard cells are configured sideby side on the Y direction. The integrated circuit 180 includes ann-type doped well region (N-well) 190 and a p-type doped well region(P-well) 192, being separated by the dashed line 194. Fin active regions196 and 198 are defined by and surrounded by the isolation features(such as STI features). Particularly, the fin active regions 196 areformed in the N-well 190 and the fin active regions 192 are formed inthe P-well 192. Fin active regions 196 and 198 have elongated shapes andare oriented in the Y direction. Fin active regions 196 and 198 aredesigned with discontinuous structures so that each standard cell hasits individual fin active region 196 in the N-well 190 and itsindividual fin active region 198 in the P-well 192, being separated fromfin active regions in adjacent standard cells. Thus, the boundary linesbetween the adjacent standard cells are defined on the STI features. Theintegrated circuit 180 includes various gates (also referred to as gatestacks) 110 formed on the respective fin active regions 196 and 198. Thegates 100 also have elongated shapes and are oriented in the Xdirection. The interconnection gates 114 are formed on the edges of thestandard cells to provide isolations between the adjacent standardcells. Particularly, the interconnection gates 114 are at leastpartially landing on the STI features 104. Sources 202 and drains 204are formed on the fin active regions on sides of the corresponding gates110. As noted above, the NAND logic gate 186 and the NOR logic gate 188each further include a common drain 206 and a common active region 208.The sources 202, drains 204, common drains 206 and common active regions208 are formed by introducing dopants into the respective fin activeregions using suitable technologies, such as ion implantation. In thepresent embodiment, the sources 202, drains 204, common drains 206 andcommon active regions 208 in the N-well 190 include p-type dopant, suchas boron while the sources 202, drains 204, common drains 206 and commonactive regions 208 in the P-well 192 include n-type dopant, such asphosphorus.

Those fin active regions 196 and 198, gates 110, sources 202, drains204, common drains 206 and common active regions 208 are configured toform various devices. For example, the inverter 184 includes a pFETwithin the N-well 190 and an nFET within the P-well 192; the NAND logicgate 186 includes two pFETs within the N-well 190 and two nFETs withinthe P-well 192; and the NOR logic gate 188 includes two pFETs within theN-well 190 and two nFETs within the P-well 192. For example, in theinverter standard cell 184, the fin active region 198, the source 202,the drain 204, and the gate 110 are configured to form an nFET in theP-Well 192. The integrated circuit 180 also includes various conductivefeatures configured to connect those FETs into an inverter 184, an NANDlogic gate 186 and an NOR logic gate 188. Particularly, the contactfeatures 116, via-0 features 142 and the first metal lines 132 arefurther illustrated in FIG. 11B. For simplicity, the numerals forvarious doped features (such as sources and drains) are eliminated fromFIG. 11B.

Referring to FIG. 11B, the contact features 116, the via-0 features 142,and the first metal lines 132 are formed thereon and configured tocouple various FETs. The legends for the contact features (“contact”)116, the via-0 features (“Via-0”) 142, and the first metal lines (“M1”)132 are provided in the bottom portion of FIG. 11B for bettercomprehending those features. The first metal lines 132 are connected tothe sources and drains through the contact features 116 and the via-0features 142. The first metal lines 132 are oriented in the Y direction.

Referring to FIG. 11C, the via-1 features 144, the second metal lines134, the via-2 features 146, and the third metal lines 136 are furtherillustrated in FIG. 11C. The via-1 features 144, the second metal lines134, the via-2 features 146, and the third metal lines 136 are formedthereon and connected to underlying features to the integrated circuit180. The legends for the via-1 features (“Via-1”) 144, the second metallines (“M2”) 134, the via-2 features (“Via-2”) 146, and the third metallines (“M3”) 136 are provided in the bottom portion of FIG. 11C forbetter comprehending those features. The second metal lines 134 areconnected to the first metal lines 132 through the via-1 features 144.The third metal lines 136 are connected to the second metal lines 134through the via-2 features 146. The second metal lines 134 are orientedin the X direction and the third metal lines 136 are oriented in the Ydirection.

As noted above, those gates, contact features, via features and metallines are configured with dimensions, pitches, and width as described inthe semiconductor structure of FIG. 1. Those contact features, viafeatures and metal lines are routed to connect various gates, sourcesand drains to form various logic gates that include the inverter 184,NAND 186 and NOR 188. The Inverter 184, NAND 186 and NOR 188 are furtherillustrated in FIG. 12 in schematic view to show various connections. Inthe present embodiment, the inverter 184 includes one nFET and one pFET(labeled as “nFET” and “pFET”, respectively, in FIG. 12); the NAND 186includes two nFETs and two pFETs (labeled as “nFET1”, “nFET2”, “pFET1”,and “pFET21”, respectively, in FIG. 12); and the NOR 188 includes twonFETs and two pFETs (labeled as “nFET1”, “nFET2”, “pFET1”, and “pFET21”,respectively, in FIG. 12). Those nFETs and pFETs are connected asillustrated in FIG. 12 to form the inverter 184, NAND 186 and the NOR188, respectively. Furthermore, each of the NAND 186 and NOR 188includes a common drain and a common active region (“common OD”). Highand low power lines are referred to as “Vdd” and “Vss”, respectively, inFIG. 12.

FIG. 13 is a top view of an integrated circuit 200 constructed accordingto various aspects of the present disclosure in one embodiment. Theintegrated circuit 200 is another embodiment of the semiconductorstructure 100 or the semiconductor structure 160. Various metal linesand gates are oriented, configured and designed with dimension asdescribed in the semiconductor structure 100 or 160. For example, thethickness of the second metal lines 134 is greater than the thickness ofthe first metal lines 132 and the thickness of the third metal lines136.

The integrated circuit 200 includes various standard cells configuredside by side along the Y direction. The integrated circuit 200 includesmultiple standard cells with cell boundary lines presented by the dashedlines 182. In the present embodiment, the integrated circuit 200includes a first standard cell 184 having an inverter; a second standardcell 186 having an NAND logic gate; and a third standard cell 188 havinga NOR logic gate. The integrated circuit 200 is similar to theintegrated circuit 180 of FIG. 11C but with some differences describedbelow.

The interconnection gates 114 in the integrated circuit 180 of FIG. 11Aare replaced by dielectric gates 212. The fin active regions 196 and 198are still discontinuous structures. The dielectric gates 212 are formedon the cell boundary lines 182 and are landing on the STI features 104.The dielectric gates 212 provide isolation function to the adjacentstandard cells. The dielectric gates 212 are dielectric features withoutelectrical connection. The dielectric gates 212 include one or moresuitable dielectric material, such as silicon oxide, silicon nitride,silicon oxynitride, low-k dielectric material, other suitable dielectricmaterial, or a combination thereof. In some embodiments, the dielectricgates 212 are formed by a procedure described below. In the formation ofthe gates 110 (and the interconnection gates 114 as well), polysilicongates are first formed by deposition and patterning (wherein thepatterning further includes lithography process and etching); after thesource and drain features are formed, and an interlayer dielectricmaterial is deposited; and the polysilicon are replaced by metal gate.The dielectric gates 212 are formed in a similar procedure but thecorresponding polysilicon gates are replaced separately by one or moredielectric material instead of conductive materials used to form themetal gates. Particularly, after the corresponding polysilicon gates areformed, the interlayer dielectric material is deposited; the polysilicongates are removed by etching, forming gate trenches in the interlayerdielectric material; and the dielectric material(s) are deposited in thegate trenches to form dielectric gates 212. A CMP process may be furtherapplied to remove excessive dielectric material(s) on the interlayerdielectric material. So the dielectric gates 212 do not function asgates but as isolation features.

FIG. 14 is a top view of an integrated circuit 220 constructed accordingto various aspects of the present disclosure in one embodiment. Theintegrated circuit 220 is another embodiment of the semiconductorstructure 100 or the semiconductor structure 160. Various metal linesand gates are oriented, configured and designed with dimension asdescribed in the semiconductor structure 100 or 160. For example, thethickness of the second metal lines 134 is greater than the thickness ofthe first metal lines 132 and the thickness of the third metal lines136.

The integrated circuit 220 includes various standard cells configuredside by side along the Y direction. The integrated circuit 220 includesmultiple standard cells with cell boundary lines presented by the dashedlines 182. In the present embodiment, the integrated circuit 220includes a first standard cell 184 having an inverter; a second standardcell 186 having an NAND logic gate; and a third standard cell 188 havinga NOR logic gate. The integrated circuit 200 is similar to theintegrated circuit 200 of FIG. 13 but with some differences describedbelow.

Firstly, the fin active region 196 in the N-well 190 and the fin activeregion 198 in the P-well 192 are continuous structure and extend throughmultiple standard cells, such as through the inverter 184, the NANDlogic gate 186 and the NOR logic gate 188 in the present example. Thedielectric gates 212 in the integrated circuit 180 of FIG. 13 arereplaced by gates 222. The gates 222 are functional gates, similar tothe gates 110 in terms of formation and composition. For example, thegates 222 are simultaneously formed with the gates 110 in the sameprocedure that includes forming polysilicon gates, and then replacingthe polysilicon gates with metal gates. The gates 222 also include highk dielectric material for gate dielectric and metal for gate electrode.However, the gates 222 are configured in the standard cell boundarylines to provide isolation between the adjacent standard cells and alsoreferred to as isolation gates 222.

Secondly, since the fin active regions 196 and 198 are continuousstructures, the gates 222 are also formed on the fin active regions 196and 198. Thus, the gates 222, with adjacent source and drain featuresand underlying channels, constitute field-effect transistors. The gates222 are connected to the power lines. Thus configured FETs associatedwith the gates 222 biased to power lines provide proper FET isolationbetween adjacent standard cells. Those FETs are also referred to asisolation FETs.

Thirdly, the gates 222 also oriented in the X direction and arediscontinuous the N-well 196 to the P-well 198, as illustrated in FIG.14. Thus, the gates 222 in the N-well 196 are connected to the highpower line Vdd, and the associated isolation FETs are pFETs; and thegates 222 in the P-well 198 are connected to the low power line Vss, andthe associated isolation FETs are nFETs.

FIG. 15 is a top view of an integrated circuit 230 constructed inaccordance with some embodiments. The integrated circuit 230 includesmultiple standard cells configured into a standard cell array. Theintegrated circuit 230 is one embodiment of the semiconductor structure100 or 160. Various metal lines and gates are oriented, configured anddesigned with dimension as described in the semiconductor structure 100or 160. For example, the thickness of the second metal lines 134 isgreater than the thickness of the first metal lines 132 and thethickness of the third metal lines 136.

Particularly, the integrated circuit 230 includes a P-well 232 and twoN-wells 234 with the P-well interposed between. Various pFETs are formedin the N-wells 234 and various nFETs are formed in the P-well 232. ThosepFETs and nFETs are configured and connected to form various standardcells 236 in array. Those standard cells may include different numbersof FETs and have different dimensions. In the present embodiment, theintegrated circuit 230 includes ten standard cells 236 (labeled to“Circuit-1”, “Ciorcuit-2”, and etc.). For example, the first standardcell includes two fin devices, such as two complimentary FETs (or twoCMOSFETs), each complimentary FET includes an nFET formed in the P-well232 and a pFET formed in the N-well 234. Those standard cells areconfigured in an abutment mode. With such a configuration, the standardcells can be arranged more efficiently with high packing density.

In various embodiments, the standard cells include logic gates, such asan inverter, an NAND logic gate, NOR logic gate. However, the standardcells are not limited to those and may include other standard cells.Those standard cells may be further configured and connected to formanother standard cell with a circuit with a different function. Forexample, a standard cell may be a flip-flop device. FIG. 16 illustratesschematic views of a flip-flop device according two embodiments. Theflip-flop device 240 is formed by two NOR logic gates cross-coupledtogether according to one embodiment. The flip-flop device 242 is formedby two NAND logic gates cross-coupled together according to anotherembodiment.

Various embodiments are described above, some variations, or alternativemay present. As noted before, the gates 110 in the semiconductorstructure 100 may be formed by a gate-replacement procedure. The gates110 and the gate-replacement procedure are further described accordanceto some embodiments.

First, one or more dummy gate stack is formed on the semiconductorsubstrate 102. The dummy gate stack includes a gate dielectric layer anda gate conductive layer on the gate dielectric layer. The formation ofthe dummy gate stack includes deposition and patterning. The patterningfurther includes lithography process and etching. A hard mask layer maybe further used to pattern the dummy gate stack. In some examples, thegate dielectric layer of the dummy gate stack includes a high kdielectric material layer formed on the semiconductor substrate 102. Acapping layer may be formed on the gate dielectric layer. A polysiliconlayer as the gate conductive layer is formed on the capping layer. Thegate dielectric layer may further include an interfacial layer (IL)interposed between the semiconductor substrate 102 and the high kdielectric material layer. In various examples, the interfacial layermay include silicon oxide formed by a proper technique, such as anatomic layer deposition (ALD), thermal oxidation or UV-Ozone Oxidation.The interfacial layer may have a thickness less than 10 angstrom. Thehigh-k dielectric layer may include metal nitrides or other metal oxides(such as HfO2) and may be formed by a suitable process such as ALD.

The dummy gate material layers are further patterned to form the dummygate stack by lithography patterning process and etching. A hard maskmay be further implemented to pattern the dummy gate material layers. Inthis case, the hard mask is formed on the dummy gate material layers bydeposition and pattering; and one or more etching process is applied tothe gate material layers through the openings of the hard mask. Theetching process may include dry etching, wet etching or a combinationthereof.

In some embodiments, the source and drain may further include lightdoped drain (LDD) features 262 formed on the substrate 102 and heavilydoped source and drain (S/D) features 264 (with the same typeconductivity and a doping concentration greater than that of the LDDfeatures), collectively referred to as source and drain. The LDDfeatures 262 and S/D features 264 are formed by respectively ionimplantation. One or more thermal annealing process is followed toactivate the doped species. In some examples, the source and drain areformed in a doped well 265 (such as an n-type doped well for a PMOS or ap-type doped well for an NMOS). In one example, a gate spacer may beformed on the sidewall of the dummy gate stack. The S/D features areformed on the substrate 102 afterward and are offset from LDD by thegate spacers.

The gate spacer 266 includes one or more dielectric material, such assilicon oxide, silicon nitride, silicon oxynitride or combinationsthereof. In one embodiment, the gate spacer 266 includes a seal spacerdisposed on the sidewall of the gate stack and a main spacer disposed onthe seal spacer, which are formed respectively by a procedure includingdeposition and etch.

In some examples, the source and drain include doping species introducedto the semiconductor substrate 102 by a proper technique, such as ionimplantation. In some examples, the source and drain are formed byepitaxy growth to enhance device performance, such as for strain effectto enhance mobility. In furtherance of the embodiments, the formation ofthe source and drain includes selectively etching the substrate 102 toform the recesses; and epitaxy growing a semiconductor material in therecesses to form the S/D features 264. The recesses may be formed usingwet and/or dry etch process to selectively etch the material of thesubstrate 102, with proper etchant(s), such as carbon tetrafluoride(CF4), tetramethylammonium hydroxide (THMA), other suitable etchant, ora combination thereof. Thereafter, the recesses are filled with asemiconductor material by epitaxially growing S/D features 412 incrystalline structure. The epitaxy growth may include in-situ doping toform S/D with proper dopant. In yet another embodiment, silicidefeatures may be further formed on the source and drain regions to reducethe contact resistance. The silicide features may be formed by atechnique referred to as self-aligned silicide (salicide) includingmetal deposition (such as nickel deposition) onto a silicon substrate, athermal anneal to react the metal with silicon to form silicide, and anetch to removed un-reacted metal.

An interlayer dielectric material (ILD) 268 is formed on the substrateand the dummy gate stack. The ILD 268 is deposited by a propertechnique, such as CVD. The ILD 268 includes a dielectric material, suchas silicon oxide, low k dielectric material or a combination. Then achemical mechanical polishing (CMP) process may be applied thereafter topolarize the surface of the ILD 268. In one example, the dummy gatestack is exposed by the CMP process for the subsequent processing steps.

The dummy gate stack is completely or partially removed, resulting in agate trench in the ILD 268. The removal of the dummy gate stack includesone or more etching steps to selectively remove various gate materiallayers of the dummy gate stack using a suitable etching process, such asone or more wet etch, dry etch or a combination thereof.

Thereafter, various gate material layers are filled in the gate trench,forming a metal gate 110 in the gate trench. In some embodiments such asin high-k last process, the gate material layers includes a gatedielectric layer 270 and a gate conductive layer (or gate electrode)272. The gate dielectric layer 270 includes a high-k dielectricmaterial. The gate conductive layer 272 includes metal. In someembodiments, the gate conductive layer 272 include multiple layers, suchas a capping layer, a work function metal layer, a blocking layer and afilling metal layer (such as aluminum or tungsten). The gate materiallayers may further include an interfacial layer 274, such as siliconoxide, interposed between the substrate 102 and the high-k dielectricmaterial. The interfacial layer 274 is a portion of the gate dielectriclayer. The various gate material layers are filled in the gate trench bydeposition, such as CVD, PVD, plating, ALD or other suitable techniques.The high-k dielectric layer 270 includes a dielectric material havingthe dielectric constant higher than that of thermal silicon oxide, about3.9. The high k dielectric layer 270 is formed by a suitable processsuch as ALD. Other methods to form the high k dielectric material layerinclude MOCVD, PVD, UV-Ozone Oxidation or MBE. In one embodiment, thehigh k dielectric material includes HfO2. Alternatively, the high kdielectric material layer 270 includes metal nitrides, metal silicatesor other metal oxides.

An operation may be applied to remove excessive gate materials andplanarize the top surface. For example, a CMP process may be applied toremove the excessive gate materials. After the CMP process, the topsurface of the semiconductor structure 100 is planarized. In the presentexample, various features, including gate 110, source and drain (264)are formed and configured as a field-effect transistor 280.

The gate 110, as described above, may include additional materiallayers. For example, the gate electrode 272 includes a capping layer, ablocking layer, a work function metal layer, and a filling metal layer.In furtherance of the embodiments, the capping layer includes titaniumnitride, tantalum nitride, or other suitable material, formed by aproper deposition technique such as ALD. The blocking layer includestitanium nitride, tantalum nitride, or other suitable material, formedby a proper deposition technique such as ALD. In various embodiments,the filling metal layer includes aluminum, tungsten or other suitablemetal. The filling metal layer is deposited by a suitable technique,such as PVD or plating. The work functional metal layer includes aconductive layer of metal or metal alloy with proper work function suchthat the corresponding FET is enhanced for its device performance. Thework function (WF) metal layer is different for a pFET and a nFET,respectively referred to as an n-type WF metal and a p-type WF metal.The choice of the WF metal depends on the FET to be formed on the activeregion. In some embodiments, the n-type WF metal includes tantalum (Ta).In other embodiments, the n-type WF metal includes titanium aluminum(TiAl), titanium aluminum nitride (TiAlN), or combinations thereof. Inother embodiments, the n-metal include Ta, TiAl, TiAlN, tungsten nitride(WN), or combinations thereof. The n-type WF metal may include variousmetal-based films as a stack for optimized device performance andprocessing compatibility. In some embodiments, the p-type WF metalincludes titanium nitride (TiN) or tantalum nitride (TaN). In otherembodiments, the p-metal include TiN, TaN, tungsten nitride (WN),titanium aluminum (TiAl), or combinations thereof. The p-type WF metalmay include various metal-based films as a stack for optimized deviceperformance and processing compatibility. The work function metal isdeposited by a suitable technique, such as PVD.

Even though only one gate 110 is shown in the figures, however, multiplegate stacks are formed on the substrate 102 for various correspondingnFETs, pFETs and other circuit devices. In some embodiments, the gate110 is formed on the 3D fin active region and is a portion of a FinFET.

The present disclosure provides various embodiments of a logic circuitand a layout with a multiple metal layer structure and manufacturingmethod, wherein one or more of the dimensional parameters (thickness,pitch and width) of the second metal lines are greater than thecorresponding dimensional parameters of the first and third metal lines.Various advantages may present in various embodiments. By utilizing thedisclosed metal configuration layout, the logic circuit has a highpacking density. Other advantages may present in various embodiments ofthe semiconductor structure 100. For examples, with the reducedthicknesses and pitches of the first metal lines 132 and the third metallines 136, the routing efficiency is increased; the intra-cell couplingcapacitance and the power lines resistance are reduced; chip packingdensity is increased; large pitches are minimized due to the minimumpitch of the second metal lines 134 are substantially aligned with thatof the gates 110; and the circuit speed is improved.

Thus, the present disclosure provides a semiconductor structure inaccordance with some embodiments. The semiconductor structure includes asemiconductor substrate having active regions; a plurality offield-effect devices disposed on the semiconductor substrate, whereinthe field-effect devices include gate stacks with elongated shapeoriented in a first direction; a first metal layer disposed over thegate stacks, wherein the first metal layer includes a plurality of firstmetal lines oriented in a second direction that is orthogonal to thefirst direction; a second metal layer disposed over the first metallayer, wherein the second metal layer includes a plurality of secondmetal lines oriented in the first direction; and a third metal layerdisposed over the second metal layer, wherein the third metal layerincludes a plurality of third metal lines oriented in the seconddirection. The first metal lines have a first thickness T₁, the secondmetal lines have a second thickness T₂, and the third metal lines have athird thickness T₃. The second thickness is greater than the firstthickness and the third thickness.

The present disclosure provides a semiconductor structure in accordancewith some other embodiments. The semiconductor structure includes asemiconductor substrate having a first region for a first standard celland a second region for a second standard cell, wherein each of thefirst and second standard cells includes a n-type field-effecttransistor and a p-type field effect transistor; a first active regionand a second active region formed on the semiconductor substrate,wherein the first and second active regions are isolated from each otherby an isolation feature, and wherein the first and second standard cellsshare an edge on the isolation feature; a first and second gate stackswith elongated shape oriented in a first direction, wherein the firstgate stack is disposed on the first active region and the second gatestack is disposed in the second active region; a first and secondinterconnection gate stacks oriented in the first direction, wherein thefirst interconnection gate stack is partially landing on the firstactive region and partially landing on the isolation feature, and thesecond interconnection gate stack is partially landing on the secondactive region and partially landing on the isolation feature; a firstmetal layer disposed over the first and second gate stacks, wherein thefirst metal layer includes a plurality of first metal lines oriented ina second direction being orthogonal to the first direction; a secondmetal layer disposed over the first metal layer, wherein the secondmetal layer includes a plurality of second metal lines oriented in thefirst direction; and a third metal layer disposed over the second metallayer, wherein the third metal layer includes a plurality of third metallines oriented in the second direction. The first metal lines have afirst thickness T₁, the second metal lines have a second thickness T₂,the third metal lines have a third thickness T₃, and a first thicknessratio T₂/T₁ is greater than 1.2, a second thickness ratio T₂/T₃ isgreater than 1.2. The semiconductor structure includes a semiconductorsubstrate having active regions; a plurality of field-effect devicesdisposed on the semiconductor substrate, wherein the field-effectdevices include gate stacks with elongated shape oriented in a firstdirection; a first metal layer disposed over the gate stacks and havinga first thickness T₁, wherein the first metal layer includes a pluralityof first metal lines oriented in a second direction that is orthogonalto the first direction; a second metal layer disposed over the firstmetal layer and having a second thickness T₂, wherein the second metallayer includes a plurality of second metal lines oriented in the firstdirection; a third metal layer disposed over the second metal layer andhaving a third thickness T₃, wherein the third metal layer includes aplurality of third metal lines oriented in the second direction; afourth metal layer disposed over the third metal layer and having aforth thickness T₄, wherein the fourth metal layer includes a pluralityof fourth metal lines oriented in the first direction; a fifth metallayer disposed over the forth metal layer and having a fifth thicknessT₅, wherein the fifth metal layer includes a plurality of fifth metallines oriented in the second direction; a sixth metal layer disposedover the fifth metal layer and having a sixth thickness T₆, wherein thesixth metal layer includes a plurality of sixth metal lines oriented inthe first direction; first via features vertically connecting betweenthe first metal lines and the second metal lines; second via featuresvertically connecting between the second metal lines and the third metallines; third via features vertically connecting between the third metallines and the fourth metal lines; fourth via features verticallyconnecting between the fourth metal lines and the fifth metal lines; andfifth via features vertically connecting between the fifth metal linesand the sixth metal lines. A first thickness ratio T₂/T₁ is greater than1.2; a second thickness ratio T₂/T₃ is greater than 1.2; a thirdthickness ratio T₅/T₂ is greater than 1.2; a forth thickness ratio T₆/T₅is less than 1.1; and the fourth via features have a first width and thefifth via features have a second width, and a ratio of the second widthover the first width is greater than 1.5.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A device comprising: a substrate having a firstregion and a second region; a first active region disposed in the firstregion of the substrate; a second active region disposed in the secondregion of the substrate; a first gate stack disposed over the firstactive region and a second gate stack disposed over the second activeregion, wherein the first gate stack and the second gate stack haveelongated shapes oriented in a first direction; a first dielectric gatestack disposed between the first region and the second region of thesubstrate, the first dielectric gate stack electrically isolating thefirst region from the second region of the substrate; a first metallayer disposed over the first and second gate stacks, wherein the firstmetal layer includes a plurality of first metal lines oriented in asecond direction being orthogonal to the first direction; a second metallayer disposed over the first metal layer, wherein the second metallayer includes a plurality of second metal lines oriented in the firstdirection; and a third metal layer disposed over the second metal layer,wherein the third metal layer includes a plurality of third metal linesoriented in the second direction, and wherein the second metal lineshave a first minimum pitch P₁, wherein the first metal lines have asecond minimum pitch P₂, wherein the third metal lines have a thirdminimum pitch P₃, wherein the third minimum pitch P₃ equals to thesecond minimum pitch P₂, wherein the first minimum pitch P₁ is greaterthan the second minimum pitch P₂, and wherein the first minimum pitch P₁is greater than the third minimum pitch P₃.
 2. The device of claim 1,wherein each of the first metal lines have a first thickness T₁, whereineach of the second metal lines have a second thickness T₂, wherein eachof the third metal lines have a third thickness T₃, wherein a firstthickness ratio T₂/T₁ is equal to or greater than 1.2, and wherein asecond thickness ratio T₂/T₃ is equal to or greater than 1.2.
 3. Thedevice of claim 1, wherein the first gate stack in the first region ispart of an inverter, and wherein the second gate stack in the secondregion is part of either a NAND logic gate stack or a NOR logic gatestack.
 4. The device of claim 1, further comprising: a third activeregion disposed in a third region of the substrate; a third gate stackdisposed over the third active region; and a second dielectric gatestack disposed between the second region and the third region of thesubstrate, the second dielectric gate stack electrically isolating thesecond region from the third region of the substrate.
 5. The device ofclaim 4, wherein the first gate stack in the first region is part of aninverter, wherein the second gate stack in the second region is part ofa NAND logic gate stack; and wherein the third gate stack in the thirdregion is part of a NOR logic gate stack.
 6. The device of claim 1,further comprising: a third active region disposed in the first regionof the substrate; a dielectric isolation structure disposed on thesubstrate between the first active region and the third active region,and wherein the first gate stack extends from the first active region tothe third active region, and wherein the first gate stack disposed overthe first active region is part of a first n-type field-effecttransistor and wherein the first gate stack disposed over the thirdactive region is part of a first p-type field-effect transistor.
 7. Thedevice of claim 1, further comprising: a fourth active region disposedin the second region of the substrate; the dielectric isolationstructure disposed on the substrate between the second active region andthe fourth active region, and a third gate stack disposed over thesecond active region and extending to the fourth active region, whereinthe second gate stack extends from the second active region to thefourth active region, and wherein the second gate stack disposed overthe second active region is part of a second n-type field-effecttransistor and wherein the second gate stack disposed over the fourthactive region is part of a second p-type field-effect transistor, andwherein the third gate stack disposed over the second active region ispart of a third n-type field-effect transistor and wherein the thirdgate stack disposed over the fourth active region is part of a thirdp-type field-effect transistor.
 8. The device of claim 1, wherein atleast one of the first metal lines has a first thickness T₁, wherein atleast one of the second metal lines has a second thickness T₂, whereinat least one of the third metal line has a third thickness T₃, andwherein the second thickness T₂ is greater than the first thickness T₁and wherein the second thickness T₂ is greater than the third thicknessT₃.
 9. The device of claim 1, wherein the second metal lines have afirst width W₁, and wherein the first gate includes a plurality of firstgates having a second width W₂ and a fourth minimum pitch P₄, andwherein the fourth minimum pitch P₄ is different than first minimumpitch P₁ of the second metal lines.
 10. A device comprising: a substratehaving a first region, a second region and a third region; a firstactive region disposed in the first region of the substrate; a secondactive region disposed in the second region of the substrate; a thirdactive region disposed in the third region of the substrate; a firstgate stack disposed over the first active region in the first region, asecond gate stack disposed over the second active region in the secondregion and a third gate stack disposed over the third active region inthe third region, wherein the first gate stack, the second gate stackand the third gate stack have elongated shapes oriented in a firstdirection; a first metal layer disposed over the first, second and thirdgate stacks, wherein the first metal layer includes a first metal lineoriented in a second direction being orthogonal to the first direction;a second metal layer disposed over the first metal layer, wherein thesecond metal layer includes a second metal line oriented in the firstdirection; and a third metal layer disposed over the second metal layer,wherein the third metal layer includes a third metal line oriented inthe second direction, and wherein the first metal line includes aplurality of first metal lines having a first thickness T₁, the secondmetal line includes a plurality of second metal lines having a secondthickness T₂, the third metal line includes a plurality of third metallines having a third thickness T₃, and wherein the second thickness T₂is greater than the first thickness T₁ and wherein the second thicknessT₂ is greater than the third thickness T₃, wherein the second metallines have a first minimum pitch P₁, wherein the first metal lines havea second minimum pitch P₂, wherein the third metal lines have a thirdminimum pitch P₃, wherein the third minimum pitch P₃ equals to thesecond minimum pitch P₂, wherein the first minimum pitch P₁ is greaterthan the second minimum pitch P₂, and wherein the first minimum pitch P₁is greater than the third minimum pitch P₃.
 11. The device of claim 10,further comprising a first isolation gate stack disposed between thefirst region and the second region of the substrate, the first isolationgate stack connected to a first power line such that the first isolationgate stack biased to the first power line isolates the first region ofthe substrate from the second region of the substrate.
 12. The device ofclaim 11, wherein the first isolation gate stack includes a firstportion disposed over the first active region.
 13. The device of claim10, further comprising a second isolation gate stack disposed betweenthe second region and the third region of the substrate, the secondisolation gate stack connected to a second power line such that thesecond isolation gate stack biased to the second power line isolates thesecond region of the substrate from the third region of the substrate.14. The device of claim 10, wherein the first gate stack in the firstregion is part of an inverter, wherein the second gate stack in thesecond region is part of a NAND logic gate stack; and wherein the thirdgate stack in the third region is part of a NOR logic gate stack. 15.The device of claim 10, wherein at least one of the first metal lineshas a first thickness T₁, wherein at least one of the second metal lineshas a second thickness T₂, wherein at least one of the third metal lineshas a third thickness T₃, and wherein the second thickness T₂ is greaterthan the first thickness T₁ and wherein the second thickness T₂ isgreater than the third thickness T₃.
 16. The device of claim 10, whereinthe second metal lines have a first width W₁, and wherein the first gateincludes a plurality of first gates having a second width W₂ and afourth minimum pitch P₄, and wherein the fourth minimum pitch P₄ isdifferent than first minimum pitch P₁ of the second metal lines.
 17. Adevice comprising: a substrate having a first region, a second regionand a third region; an inverter disposed on the first region of thesubstrate; a logic NAND gate stack disposed on the second region of thesubstrate; a logic NOR gate stack disposed on the third region of thesubstrate; a first gate stack disposed between the first region and thesecond region of the substrate, the first gate stack contributing toelectrically isolating the first region from the second region; a secondgate stack disposed between the second region and the third region ofthe substrate, the second gate stack contributing to electricallyisolating the second region from the third region, wherein the firstgate stack and the second gate stack have elongated shapes oriented in afirst direction; a first metal layer disposed over the first and secondgate stacks, wherein the first metal layer includes a plurality of firstmetal lines oriented in a second direction being orthogonal to the firstdirection; a second metal layer disposed over the first metal layer,wherein the second metal layer includes a plurality of second metallines oriented in the first direction; and a third metal layer disposedover the second metal layer, wherein the third metal layer includes aplurality of third metal lines oriented in the second direction, andwherein the second metal lines have a first minimum pitch P₁, whereinthe first metal lines have a second minimum pitch P₂, wherein the thirdmetal lines have a third minimum pitch P₃, wherein the third minimumpitch P₃ equals to the second minimum pitch P₂, wherein the firstminimum pitch P₁ is greater than the second minimum pitch P₂, andwherein the first minimum pitch P₁ is greater than the third minimumpitch P₃.
 18. The device of claim 17, wherein each of the first metallines have a first thickness T₁, wherein each of the second metal lineshave a second thickness T₂, wherein each of the third metal lines have athird thickness T₃, wherein a first thickness ratio T₂/T₁ is equal to orgreater than 1.2, wherein a second thickness ratio T₂/T₃ is equal to orgreater than 1.2, and wherein a third thickness ratio T₃/T₁ equals to 1.19. The device of claim 17, wherein the first gate stack is a firstdielectric gate stack and the second gate stack is a second dielectricgate stack.
 20. The device of claim 17, wherein the first gate stack isa first isolation gate stack, the first isolation gate stack connectedto a first power line such that the first isolation gate stack biased tothe first power line isolates the first region of the substrate from thesecond region of the substrate.